The removal of oil from admixture with water has posed a problem in many industries for many years. For example, an immediate problem exists in oil fields where water has to be separated from oil in order for the oil to be usable. This is particularly a vital problem where water or steam is injected into the well to aid in the oil extraction process. Also, previously known processes could not effectively separate light oils, such as kerosene, from admixture with water.
Attempts have been made to remove water from oil-water emulsions or mixtures by the utilization of sand filters. It has been discovered that sand filters fail after a short period of operation and the sand media has to be replaced, due to the building of "mud balls" or mixtures of dirt, oil and water in the sand. These mud balls do not float out or break-up during the normal backwash of the filters, and the sand cannot be reused. It has now been determined that sand, although normally considered a highly hydrophilic and highly oleophobic filter medium, does not reject entrapped oil from the sand surface to a sufficient extent to accommodate effective backwashing. There exists a need for a filter medium which can reject accumulated oil more easily and more completely than does sand.
In my earlier U.S. Pat. Nos. 3,780,861 and 3,992,291, I have proposed the specific utilization of a filter bed composed of granulated shells of black walnuts (Juglans Nigra L.) as a filter medium for removing solid contaminents or oil from liquids.
As disclosed in my earlier patents, the filter bed preferably was cleaned -by violently and turbulently backwashing over a perforated element with at least a portion of the contaminents being withdrawn through the perforated element as the filter medium together with the contaminents were flowed thereover, all as described in my earlier U.S. Pat. No. 3,550,774. For use in such cleaning processes, the particles must be on the order of 20-30 mesh to avoid clogging or by-passing of the perforate element.